| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 101 === In this study, an apparatus which can be operated at low temperature and high pressure conditions was set up to measure the hydrate-liquid water-vapor (H-Lw-V) three-phase dissociation conditions of methane hydrate in the presence of additives by employing the isochoric method. The certain additives to system of methane + water were investigated for their effects on the phase boundary of methane hydrate. Also, the kinetic behavior of methane hydrate was investigated in an isochoric system to see how factors (e.g. sub-cooling temperature, experimental pressure) would affect the formation kinetics of methane hydrate.
In this work, Cyclopentanone and 4-Hydroxy-4-methyl-2-pentanone were chosen as additives. The addition of Cyclopentanone in methane hydrate system shifted hydrate phase boundaries to lower pressure and higher temperature and thus the hydrate stability region was broadened, therefore it had a promotion effect on the formation of methane hydrate. Furthermore, the promotion effect increased when the concentration of Cyclopentanone in hydrate system increased. With 15 wt% Cyclopentanone, the equilibrium temperature increaseed about 11 K at given pressure in comparison to that of pure water system. On the other hand, the results of adding 4-Hydroxy-4-methyl-2-pentanone showed the inhibition effect on the formation of methane hydrate. Similarly, the inhibition effect increased when the concentration of 4-Hydroxy-4-methyl-2-pentanone in hydrate system increased. With 30 wt% 4-Hydroxy-4-methyl-2-pentanone, the equilibrium temperature decreases about 4 K at given pressure in comparison to that of pure water system. In addition, 3.5 wt% NaCl(aq) was used as brine solution to simulate the salinity of the seawater environment. The dissociation conditions of methane hydrate in brine were also measured in this study with the addition of Cyclopentanone and 4-Hydroxy-4-methyl-2-pentanone.
In the formation kinetics of methane hydrate, Cyclopentanone seems that it could shorten the induction time needed for hydrate formation so Cyclopentanone was chosen as additive. The results showed that Cyclopentanone could reduce the induction time in comparison to that of pure water system, and the initial rate of hydrate formation was effectively increased by adding Cyclopentanone. In conclusion, Cyclopentanone was an effective kinetic promoter to form methane hydrate in this work.
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